It is common in the use of rotationally actuated valves, such as rotary plug valves and butterfly valves, to employ an actuator that resolves a linear actuator translation into a rotational moment. This rotation is used to open and close the valve gate or plug. One such rotary valve is shown and described in U.S. Pat. No. 5,305,987 to Baumann. In this patent, a linkage is provided at the end of the shaft. This linkage is interconnected with a linear actuating device. Such actuators often include large mechanical housings that receive air and cause translation of the linear actuator component by interaction with a rolled diaphragm that moves in response to applied pressure. The housing is supported relative to the valve casing by a large framework that provides room for the required linkages to move.
The above-outlined approach to constructing a rotary valve unit is effective but requires a good deal of space around the actual valve casing for the actuator mechanism. Similarly, the actuator mechanism is relatively complex and, thus, is expensive to construct and service. Servicing itself is difficult because the housing must be assembled and disassembled under the pressure of a long compression spring. The assembly and disassembly requires the respective attachment and removal of several bolts and other components.
It has also been recognized that the linkages that resolve linear translation into rotational shaft movement are often prone to backlash and/or may be difficult to assemble onto a shaft. Many rotary valve shafts have a square cross section which can create backlash if the linkage is not accurately sized to the shaft. A splined shaft would reduce backlash, but would make misalignment of the linkage more likely since the linkage can be positioned in a large number of rotational orientations. However, a square cross section is more prone to enable play between the linkage and the shaft as the linkage is rotated to, in turn, rotate the shaft. The use of set screws or complicated clamps to increase the strength between the linkage and the shaft have been contemplated, but these structures add to the complexity of the interconnection between components and thus increase costs in assembly time for a valve. U.S. Pat. No. 4,345,850 to Baumann teaches a novel rotary valve linkage arrangement in which moments are generated in each of two opposing arms that "jam" the two arms into firm engagement with the square shaft end. The application of this linkage arrangement is limited to instances in which the two arms are in relatively close proximity to each other since the arms must bear against each other to generate the necessary moment for a secure engagement. It is thus desirable to provide a linkage that firmly engages a shaft and yet enables a greater spacing between arm sections.
It is therefore an object of this invention to provide a rotary valve actuator assembly that is reliable, easy to maintain and that occupies less space than a more conventional actuator. The actuator should be usable with a variety of types of rotary valves and should enable rotation in each of opposing directions with relative accuracy. The actuator should generate sufficient torque to power most small to midsize valves. A linkage that can be used in conjunction with the actuator should enable firm engagement of a square or otherwise shaped shaft when two or more arms of the linkage are spaced at a predetermined distance from each other.